package bishi.yuxin;

import java.util.Scanner;

public class demo1 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        long sum  = 1;
        while(n >= 1) {
            sum *= n;
            n = n - 1;
        }
        String s = String.valueOf(sum);
        int ret = 0;
        for(int i = 0;i < s.length();i++) {
            if(s.charAt(i) == '0') {
                ret++;
            }
        }
        System.out.println(ret);
    }
}
